SILLION BUG issue on ADC and get around required 16F1947 rev 2 silicon

[longpole001]

rereading the methods to get around the problem option 1 actully looks the best way , but i am not sure how to do this

but it appears that by setting the ADC f/OSC conversion clock to the FRC internal , then putting the CPU into low power mode ( SLEEP mode ) , then doing a sample , then exit low power mode (SLEEP mode) by using the watchdog timer ( no other way i can see to make sleep mode exit)

i am guessing this may work but not sure ,

1. set up watchdog timer to be enabled by software bit ( _WDTE_SWDTEN ) ;WDT controlled by the SWDTEN bit in the WDTCON register) in config1 word
2. set WDTCON with 1ms timeout and enable watchdog timer lowest time
3. do asm command of sleep - to enter low power mode ( NAP 0 = too long a time about 18ms)
4. do adcin command which should complete a sample in 1.6uS
5.turn off watchdog timer

so the assumption is that the adcin command will work in low power mode and sample will complete in a max of 1ms

test to see !!!!!!!!!!!!

but anyone else can advise then please do

Cheers sheldon


item 1

' config for 16F1947
    #CONFIG
;----- CONFIG1 Options --------------------------------------------------
    __config _CONFIG1, _FOSC_INTOSC & _WDTE_SWDTEN & _PWRTE_ON & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_OFF & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF


;----- CONFIG2 Options --------------------------------------------------
    __config _CONFIG2, _LVP_OFF & _BORV_HI & _STVREN_ON & _PLLEN_ON & _WRT_OFF & _VCAPEN_OFF 
    #ENDCONFIG

item 2 - 5

  ADCON0 =  %00010001           ' enable ADC AN4 , ADCON1 setup at start of program 
   
   y = 0                          ' ensure 0
  While Y < 10                    ' do 10 voltage reads
                                  ' silicon bug in rev2 of 16F1947 , requires ADC to be done in lowpower mode and with FDC osc clock internal
    WDTCON = %00000001            ' start watchdog timer set for 1ms so that sleep mode is exit after doing adcin commands
    asm
     SLEEP                        ;'Put cpu into low power mode  
    endasm
    ADCIN 4 ,Value                 ' Read PortA.5 value into variable , this applies the fixed voltage ref (via ADCON0,ADCON1,FVRCON)
    WDTCON = %00000000             ' stop  watchdog timer after  adcin commands
    gosub Average                  ' Go do running average of ADC reading
    y = y+1                        ' Increment loop counter
  wend

[Darrel Taylor]

That won't work, since it will have to wake from sleep before running the ADCIN command.

I might suggest something like this...
It doesn't work in the simulator, but hopefully it will work on real hardware.

It uses the ADIF interrupt to wake from sleep. With the FRC clock, it only takes 48uS to complete a conversion.
Waiting for the WDT is going to take 1000uS or more.
The WDT is enabled just in case the conversion doesn't complete, but the ADIF should always wake it up first.

It assumes you are using other interrupts, and disables them accordingly.

#CONFIG
    __config  _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_ON & _CLKOUTEN_OFF & _IESO_ON & _FCMEN_ON
    __config  _CONFIG2, _WRT_OFF & _PLLEN_ON & _STVREN_ON & _BORV_19 & _LVP_OFF
#ENDCONFIG
OSCCON = %11110000           ; 32Mhz Internal

DEFINE HSER_RCSTA 90h        ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h        ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 25         ' 19200 Baud @ 32MHz, 0.16%
DEFINE HSER_CLROERR 1        ' Clear overflow automatically

ADON      VAR ADCON0.0       ; A/D converter Enable
GoDone    VAR ADCON0.1       ; A/D conversion in progress
ADIE      VAR PIE1.6         ; A/D Interrupt Enable
ADIF      VAR PIR1.6         ; A/D Interrupt Flag
GIE       VAR INTCON.7       ; Global Interrupt Enable
GIEsave   VAR BIT            ; Saves state of GIE

ADchan    VAR BYTE           ; Current A/D channel
ADvalue   VAR WORD           ; A/D result

ADCON1 = %10110000           ; Right Justify, FRC clock
ADON = 1

Main:
    FOR ADchan = 0 TO 16     ; Loop through all A/D channe
        ADCON0 = (ADCON0 & %11) | (ADchan << 2) ; Set Analog Channel
        PAUSEUS 20           ; Acquisition time
        GIEsave = GIE        ; Save state of Global Interrupts
        GIE = 0              ; Disable Global interrupts
        ADON = 0             ; reset A/D module
        ADON = 1
        ADIF = 0             ; Clear Analog Interrupt Flag
        ADIE = 1             ; Enable Analog Interrupt
        GoDone = 1           ; Start Analog conversion
        @ SLEEP              ; go to SLEEP
        ADIE = 0             ; Disable Analog Interrupt
        GIE = GIEsave        ; Restore Global Interrupt state
        ADvalue.HighByte = ADRESH  ; Get A/D result
        ADvalue.LowByte  = ADRESL

        HSEROUT [DEC2 ADchan," = ",DEC ADvalue,13,10]
        PAUSE 200
    NEXT ADchan
GOTO Main